3 Answers
3

Druids in AD&D were limited to the vocalization of the animal form they took. GM note: Be careful about mimics--animals that can imitate others animals. Mimics have normal vocalizations that are not speech as PCs would know it.

On a side note (but probably not of much help, since it's 2nd Edition related): The "Shapeshifter" character kit in the "Complete Druid's Handbook" allows a 7th+ level druid to change portions of her body (i.e. sprout wings, grow fangs, etc.), which would suggest that, in an animal form, she'd be capable of transforming her vocal chords to allow human speech.